The parameters examined were both chem-ical nitrogen, sulphur, magnesium, potassium, calcium, manganese, iron and lead and mor-phological needle length, flat projection, dry weight, spe
Trang 1Original article
on a limestone substrate: the role of nutritional
Enrico Cenni, Filippo Bussotti Lorenzo Galeotti
Laboratory of Applied and Forest Botany, Department of Plant Biology,
University of Florence, Piazzale delle Cascine 28, I 50144 Florence, Italy
(Received 6 June 1997; accepted 26 November 1997)
Abstract - The Austrian black pine reforestation projects on Monte Morello, near the heavily pop-ulated metropolitan area of Florence (Italy), have been affected for many years now by a severe
decline consisting of widespread crown yellowing To investigate the causes of this decline foliar diagnosis methods were used to monitor the nutritional status of ten trees, sampling and
analysing every year, between 1989 and 1992, the current year needles (c), needles from the previous year (c+ I) and from the year before that (c+2) The parameters examined were both chem-ical (nitrogen, sulphur, magnesium, potassium, calcium, manganese, iron and lead) and
mor-phological (needle length, flat projection, dry weight, specific dry weight and water content) The findings show a considerable calcium accumulation as the needles age, accompanied by an
increase in dry weight and specific dry weight, as well as a marked antagonism to manganese The influence of the nearby metropolitan area of Florence is suggested by the accumulation of lead.
(© Inra/Elsevier, Paris)
afforestation / calcium / iron / leaf senescence / manganese / Pinus nigra subsp nigra /
chlorosis
Résumé - Le dépérissement des reboisements de Pinus nigra Arn sur substrat calcaire ; le
rôle des facteurs nutritionnels étudiés à l’aide du diagnostic foliaire Les reboisements de pin noir d’Autriche dans le Monte Morello, près de l’importante zone urbaine de Florence (Italie) sont
affectés depuis maintenant plusieurs années d’un sévère dépérissement consistant en un
jaunis-sement très fréquent des couronnes Pour étudier les causes de ce dépérissement, des méthodes d’analyse foliaire ont été utilisées pour suivre l’état nutritionnel de dix arbres échantillonnés et
analysés chaque année entre 1989 et 1992, en prenant en compte les aiguilles de l’année (c), les
aiguilles de l’année précédente (c+1) et les aiguilles âgées de 2 ans (c+2) Les paramètres étudiés
étaient chimiques (azote, soufre, magnésium, potassium, calcium, manganèse, fer, plomb)
mor-*
Correspondence and reprints
Trang 2phologiques (longueur aiguilles, projetée, poids spécifique eau)
résultats montrent une accumulation considérable de calcium avec l’âge des aiguilles accompa-gnée par un accroissement du poids sec et du poids spécifique, ainsi qu’un antagonisme marqué
du manganèse L’influence de l’agglomération voisine de Florence est suggérée par l’accumulation
de plomb (© Inra/Elsevier, Paris)
reboisement / calcium / fer / sénescence foliaire / manganèse / Pinus nigra subsp Nigra / chlorose
1 INTRODUCTION
In the first half of this century, several
species of conifers were widely used in
Italy to reforest areas where the
autochthonous forest vegetation normally
consists of broadleaved trees The purpose
of these reforestation projects was usually
either timber production or
hydrogeolog-ical protection Pinus nigra Am., with all
its various subspecies, thanks to its
remarkable ecological flexibility, was one
of the species most widely used Today
the forest landscape of many Italian
regions is characterized by the presence
of stretches of conifer forests surrounded
by broadleaf woods with no apparent
land-scape and/or ecological continuity If we
further consider that these species were
often planted in environments that were
very far from their ecologically ideal
set-ting, and that they are showing all the signs
of premature senescence and ecological
instability, it is easy to understand how in
recent years a lot of discussion has been
devoted to the topic, especially the need to
allow the sites to gradually revert to a more
natural vegetation [24].
In the light of this, our paper examines
artificial Pinus nigra stands growing on
Monte Morello, in a peri-urban
environ-ment near the metropolitan area of
Flo-rence (Tuscany, central Italy), and
show-ing severe crown yellowing The purpose
of this study is to assess the vegetational
conditions by means of foliar diagnostics
[2, 4] These artificial stands, planted for
protective purposes, today still have an
important recreational function, in that
they are located in a densely urbanized
area (more than 1 million inhabitants) Thus, any conclusions drawn as to their ecological stability or instability could be
a valid contribution in guiding the deci-sions of the city’s administrators on the
fate and management of these stands
2 MATERIALS AND METHODS
2.1 Study area
Monte Morello is a mountain ridge (maxi-mum height: 934 m a.s.l.) running from NW to
SE, located immediately north-west of the urban area of Florence The prevailing litho-logical component is limestone and marl; the forest soils are for the most part shallow, rich
in skeleton and scarse in humified organic
sub-stances The mean pH of the surface layer of
the soil (0-20 cm) is 7.76; the CaCOcontent ranges from 10 % in the upper layer (0-5 cm
under the organic matter layer) to 30 % (at
10-20 cm deep) The climate is temperate, with hot summers characterized by moderately
severe droughts; the mean yearly temperature
is about 12 °C, while mean yearly rainfall ranges from 900 mm at the lower altitudes to
1 100-1 200 mm at the higher ones Monte
Morello marks the transition point between a
thermophile sub-Mediterranean flora and a mountain flora typical of the Apennines Most
of the spontaneous stands consist of mixed
deciduous xerothermal oakwoods, typical of
the sub-Mediterranean horizon, with a preva-lence of Quercus pubescens Willd and Frax-inus ornus L Anthropogenous vegetation is also very widespread, for the most part
con-sisting of conifer reforestation projects, grow-ing mainly at the higher altitudes of the
moun-tain ridge, but also present along the southern slopes of the lower hillsides These stands are
Trang 3made up of conifers, planting
pro-grammes [26] begun in 1909 and continued,
with diminishing intensity, till the early 1970s.
The purpose of all these planting programmes
was to provide hydrogeological stability in
areas with difficult pedoclimatic conditions
which were covered by secondary meadows
or by degraded broadleaf woods Today, the
artificial stands cover an area greater than 500
ha The most widely used species are Austrian
pine and laricio pine (Pinus nigra subsp nigra
and Pinus nigra subsp laricio (Poiret) Maire),
cypress (Cupressus sempervirens L.) and silver
fir (Abies alba Mill.), with a sporadic presence
of other species These stands are often
char-acterized by poor regeneration, marked
sus-ceptibility to adversities and a high degree of
inflammability Moreover, the soil they grow
on, despite the satisfactory evolution
under-gone as compared to the pre-existing situation
[3], is still poorly evolved and fairly shallow.
Black pines were used also at lower altitudes,
and in conditions that are definitely more
Mediterranean than the ecological requirements
of the species [14]
The reforestation projects on Monte Morello
were among the first stands studied in Italy for
the decline of black pines caused by unknown
agents [5] and the influence of air pollutants
was hypothesized In fact the influence of the
metropolitan area is notable primarily in the
marked acidification of the precipitations [1,
13] and in the high summertime
concentra-tions of ozone (Italian Botanical Society,
unpublished report) Thanks to the limestone
matrix of the soil, however, no phenomena of
soil acidification have been observed [30]
Moreover, as early as the 1970s, Poggesi
[26] was already reporting widespread
occur-of needle yellowing in black pines,
the poor stand conditions and insufficient mycorrhizal status This symp-tomatology is still evident today.
2.2 Sampling
The study examined ten Austrian pines, between 50 and 70 years old, two from each
of five stands along the main ridge of the mountain Needles from the upper third of the
crown were sampled from each tree: needles
that had sprouted during the sampling year (c,
needles that were about 4 months old at the time of sampling), needles from the previous year (c+1, needles aged about 16 months) and
from the year before that (c+2, needles aged about 28 months) Samples were collected for
four consecutive years, from 1989 to 1992,
always at the end of summer and following the
UN-ECE guidelines [28] Table I illustrates
the sampling protocol.
2.3 Chemical and morphological tests
Nitrogen, sulphur, calcium, magnesium, potassium, manganese, iron and lead levels
were determined Nitrogen and sulphur levels
were measured with a CHNS Element Ana-lyzer (Carlo Erba mod EA 1108) Analytical determination of the remaining elements (total
quantities) was carried out after wet digestion
in HNO (Suprapur Merck) with depositing refrigeration with an atomic absorption spec-trophotometer (Varian Spectra AA-20):
cal-cium, iron, potassium, magnesium, manganese, with flame atomization; lead in a graphite oven.
Trang 4following morphological parameters
of 100 needles were also assessed: the flat
pro-jection (Area), using a Licor LI-3100 area
meter; their fresh weight (FW) and, after
dry-ing in an oven at 60 °C till they reached a
con-stant weight, their dry weight (DW) The
fol-lowing parameters were then calculated: water
content (WC = 1 - (DW/FW)100) and specific
dry weight (SDW = DW/Area)
All data are expressed as mean values,
stan-dard deviation and correlations; a variance
analysis with ANOVA-LSD test and
discrim-inant analysis were further performed The
software used was Statistica Statsoft Inc and
SPSS for Windows 6.0.
3 RESULTS
The data in table II show the yearly
variations in the nutritional status and
mor-phology of the needles over the entire
period of the study The variance
analy-sis results (ANOVA-LSD test) show that
the values fluctuate considerably,
espe-cially the chemical parameters Table III,
hand, reports
and morphological differences between needles of different ages: the variance
analysis allows us to establish that the
majority of parameters (except needle length and the surface of the flat projection
among the morphological parameters, and magnesium concentration among the
chemical ones) displays a gradient in
cor-relation to the needle’s age: dry weight, specific dry weight and concentrations of
calcium, iron and lead all increase their
levels as the needles grow older, while the
other parameters all diminish.
The correlation between
morphologi-cal and chemical parameters were calcu-lated separately for the needles of the dif-ferent ages (c, c+1, c+2) and then globally, for the entire sample, using Spearman’s non-parametric r coefficient The
signifi-cant correlations which are of the
great-est interest within the context of this
inves-tigation are described in detail below: they
Trang 5primarily calcium,
iron and manganese.
3.1 c needles
Iron and manganese correlate inversely
to calcium (iron-calcium: no 40, r =
- 0.34, P = 0.0276; manganese-calcium:
no 40, r = -0.53, P = 0.00041) and both
elements correlate positively to each other
(no 40, r = 0.59, P = 0.00005) These
trends are visualized in figures 1 and 2
Figure 1 also shows that the
calcium-man-ganese and calcium-iron relations are
bet-ter expressed by logarithmic-type
func-tions than by linear ones Considering the
dry weight of 100 needles as a parameter
of productivity, one can observe that it
correlates inversely with both iron (no.
30, r = -0.51, P = 0.0036) and manganese
(no 30, r = -0.45, P = 0.0105).
3.2 and c+2 needles
In c+1 needles, and even more so in
c+2 needles, most of the correlations found
in c needles are no longer observable Yet,
in c+1 needles the
iron-manganese-cal-cium group behaves in a very similar man-ner to how it behaves in c needles, while
these correlations are no longer there in
c+2 needles
3.3 Needles of all ages
In order to have an equal
representa-tion of all ages examined, only the data from the samplings of 1991 and 1992 were
processed and included in the calculations
(i.e the values for 60 cases, distributed as
follows: 20 c needles, 20 c+ 1 and 20 c+2).
The correlations described above hold true
for the entire sample, except for the
cor-relation between calcium and iron which is
no longer visible In this context it is
Trang 6inter-esting to note that elements
quently accompany the ageing processes
which are expressed through a change in
specific dry weight (it increases) and/or
water content (it decreases) Calcium
cor-relates strongly with both these parameters
(no 60, Ca-WC: r=-0.58, P < 0.001;
Ca-SDW: r = 0.38, P = 0.0062), whereas iron
correlates only with specific dry weight
(no 60, r = 0.37, P = 0.0092) These
find-ings are also reported in figures 3 and 4,
where we can observe that these
correla-tions are expressed better by
exponential-type functions
Lastly, a discriminant analysis was
per-formed in order to ascertain the relative
weight of each variable considered in the
differentiation of the three needle ages In
order to select those variables that are
important in distinguishing the groups, a
stepwise selection algorithm was used: the
results are summarized in table IV There
are three elements capable of
cium, iron and manganese Calcium
(which has the lowest Wilks lambda)
con-tributes more than any other variable to
the total discrimination of the three groups;
manganese and iron follow in decreasing
order Of the two extracted canonic func-tions only the first is significant (98 % of the discriminating power is provided by
this function): it distinguishes between group 1 (c needles) and group 3 (c+2
nee-dles), where the difference between the
mean values is greatest Of the three
vari-ables, iron is the one that contributes most
to the discrimination specified by this function
4 DISCUSSION
The findings on the nutritional status
of Austrian pine needles, if compared to
the nutrional standards of this species or
Trang 7species (cf [2, 4, 19, 29]), mainly
show a considerable accumulation of
cal-cium that is more evident in c+1 and c+2
needles The increase in calcium in the
older needles is a well-known
physiolog-ical phenomenon [11], although in this
case it has undoubtedly been accentuated
by the geological matrix According to
Bergmann [2] iron and manganese also
accumulate in the older needles, but in our
findings this can only be observed in the
iron levels, and these elements (iron in c
needles, but mainly manganese) are clearly
deficient
Sulphur levels are also very low, but the concentration of this element is
com-parable to the mean values measured in Italy in a number of forest species [7, 23];
the low and diminishing levels of sulphur allow us to rule out any significant impact
of SOfrom the surrounding urbanized
areas Rather, the impact of the
Trang 8metropoli-nearby detectable high
lead concentration levels
Magnesium is constantly maintained
at optimum levels, in accordance with
other observations of this element on
lime-stone soils [2], whereas on acid soils there
are often incidences of chlorosis due to
magnesium deficiency [18] Potassium
concentrations are close to ideal levels in
c needles, but they decrease considerably
in older needles Low levels of potassium
are usual in trees growing on limestone
soils [2] An analogous behaviour of
potas-sium concentrations has been described
by Magalotti et al [23] in Pinus pinea L
needles growing on terrain characterized
by sodium alkalinity.
The decrease in concentration of some
elements is a normal feature related to the
ageing process [20] According to Schulze
[27] conifers subjected to stress
translo-cate part of their nutritional elements from
the older needles to the younger ones.
The morphological changes observed
in this study (increased specific dry weight
and reduced water content), although they
have already been observed in other
species before, are consistent with
pro-cesses of stress and/or ageing [7, 8].
Potassium, iron and manganese
defi-ciencies have been reported as inducing
needle chlorosis in trees growing mainly
on limestone soils [2, 17, 21, 27] On
lime-stone soil, in fact, calcium exerts an
antag-onistic action towards these elements,
especially against iron and manganese [2].
Sulphur deficiencies can also be
consid-ered as a factor predisposing the tree to
chlorosis [10, 21].
Especially noteworthy is the wide range
of fluctuations between one year and the
next In the 1990 sampling a higher level
of manganese and iron was detected, but
no evaluable changes in crown conditions
were observed
An analysis of the correlations between
the parameters examined suggests that
cal-cium plays decisive role, influencing
both the absorption and metabolism of
several microelements (iron and - even more so - manganese) and the processes
of foliar ageing As the needle ages, cal-cium probably accumulates in the form of oxalate crystals both inside the vacuoles
and in the apoplast, as well as in extracel-lular sites [11, 12] These processes prob-ably also cause the increase in dry weight. The findings of this study allow us to
con-clude that calcium can be considered as
’the independent ecological variable’
which exercises a dominant role over all the chemical and morphological
parame-ters.
It is interesting to observe the
differ-ent behaviour patterns of calcium,
man-ganese and iron in relation to the
senes-cence process The needle’s ageing may
be expressed by means of an increase in
specific dry weight While calcium and iron display an exponential-type positive
correlation with specific dry weight
(fig-ures 3 and 4), this does not occur with
manganese (figure 4) These findings
sug-gest that calcium exerts a greater
antago-nistic action on manganese than on iron
The former no longer cumulates in the needles after the first year of their life,
whereas the uptake and storage of the
lat-ter is continuous
5 CONCLUSIONS
The findings described above suggest
that the poor conditions of the Pinus nigra
reforestation site on Monte Morello can
be related to nutritional deficiencies and
inbalances, despite the fact that this species
is normally assumed to be sparing and
tol-erant to calcium and environmental stress
factors In fact in the study stand the trees
are growing in extreme conditions, on a
rocky limestone soil outside their ideal climate range Our findings show that
there is a considerable antagonism
Trang 9and manganese, and that
a manganese deficiency (combined with a
less marked iron deficiency) can cause
extensive leaf yellowing, a symptom
described as ’limestone chlorosis’ (cf.
[16]) The low levels of potassium and
sulphur may contribute to chlorosis
Hilbrunner and Flückiger [17] have
reported on several Abies alba Mill
refor-estation stands with marked instances of
chlorosis due to manganese deficiency In
such conditions needle chlorosis induced
by manganese deficiency is frequently
more pronounced in current-year needles
than in older needles
The fact that yearly fluctuations in the
mineral content of the needles are not
immediately reflected by significant
changes in crown conditions suggests that
the relationships among the elements are
complex and their balance plays a
funda-mental role [27], as well as the
relation-ships among elements, other
environ-mental factors and the physiological
functions of the trees.
The Monte Morello forest is very close
to a highly urbanized environment and is
affected by pollutants originating from
that area (acid rains and ozone): that may
also be important, but we still do not know
exactly how this factor interacts with the
edaphic and nutritional stresses described
above
From a more general point of view, this
study offers a further contribution to the
issues relating to the decline of artificial
coniferous reforestation sites (cf [6, 9, 15,
17, 22, 25]), especially when the
ecologi-cal compatibility between species and
stand is not ideal It is highly likely that
this type of difficulty will increase in the
future, owing to possible climate changes.
Thus, the study of naturalistic criteria to be
followed in reforestation projects becomes
a necessity not merely from the aesthetic
and landscape-planning point of view, but
also as a guarantee of the ecological
sta-bility of the plantations and, as a
conse-quence, of ability perform tions they were designed for
ACKNOWLEDGEMENTS
This study was carried out thanks to a
con-tribution by the Regione Toscana (Study on forest damage) The Authors wish to thank Mr Giulio Boschi for the sampling; Agrochimica Pisana for the chemical analyses and Dr Piero Bruschi for assistance with the statistics.
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